function Score() {
  this.score = 0
  this.x = 10
  this.y = 20

  this.draw = function (context) {
    context.font = '14px Arial'
    context.fillStyle = '#0074D2'
    context.fillText('提示：按 F 发射小球', this.x, this.y)
    context.fillStyle = '#f00'
    context.fillText('得分：' + this.score, this.x, this.y + 20)
  }

  this.plus = function () {
    this.score++
  }
}